ALERT: Geomagnetic K-index of 4 Alert issued on September 25

A Geomagnetic K-index of 4 Alert was issued on September 25, 2026. The alert was triggered when geomagnetic activity reached a K-index of 4, meeting the threshold at 21:58 UTC. The Alert is valid for the synoptic period from 21:00 to 24:00 UTC. Active warnings are currently in effect.

Potential impacts from this alert are expected primarily poleward of 65 degrees geomagnetic latitude. Weak power grid fluctuations can occur due to induced currents. Aurora may be visible in high latitude regions such as Canada and Alaska.

According to the latest NOAA SWPC forecast discussion issued at 12:30 UTC on September 25, 2026, the geomagnetic field has been largely unsettled to active, influenced by coronal hole high-speed stream (CH HSS) solar wind conditions. Solar wind speeds gradually increased, with the North-South (Bz) magnetic component showing predominantly southward orientation. These solar wind conditions are contributing to the current level of geomagnetic activity.